A1C cut points to define various glucose intolerance groups in Asian Indians

Area of Science:

• Endocrinology and Metabolism
• Clinical Diagnostics
• Epidemiology

Background:

• Hemoglobin A1C (A1C) is a key marker for glucose control, but optimal cut points for diagnosing glucose intolerance and diabetes vary across populations.
• Asian Indians exhibit a distinct pattern of glucose metabolism, necessitating population-specific diagnostic criteria.
• Existing diagnostic criteria for impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) may not accurately reflect A1C levels in this demographic.

Purpose of the Study:

• To determine specific A1C cut-off values for identifying impaired fasting glucose (IFG), impaired glucose tolerance (IGT), and diabetes in the Asian Indian population.
• To evaluate the diagnostic accuracy of A1C in comparison to established fasting plasma glucose (FPG) and 2-h postload plasma glucose criteria.

Main Methods:

• A cohort of 2,188 participants without known diabetes from the Chennai Urban Rural Epidemiology Study underwent FPG, 2-h postload glucose, and A1C measurements.
• Participants were classified using American Diabetes Association (ADA) and World Health Organization (WHO) criteria for IFG, IGT, and diabetes.
• Receiver operating characteristic (ROC) curve analysis was employed to derive optimal A1C cut points, balancing sensitivity and specificity.

Main Results:

• Optimal A1C cut points for diagnosing diabetes were identified as 6.1% (using 2-h postload glucose) and 6.4% (using FPG), demonstrating high sensitivity and specificity (88-93%).
• An A1C cut point of 5.6% was found to be optimal for identifying IGT or IFG, although its accuracy was less than 70%.
• Mean A1C levels showed a significant trend across normal glucose tolerance (5.5%), IGT (5.9%), and diabetes (8.3%), but considerable overlap existed between groups.

Conclusions:

• Specific A1C cut points of 6.1% and 6.4% are recommended for defining diabetes in Asian Indians based on 2-h postload glucose and FPG criteria, respectively.
• While an A1C of 5.6% can identify IGT or IFG, its diagnostic performance is limited, suggesting caution in its interpretation for these conditions.
• These findings underscore the importance of population-specific A1C cut points for accurate diagnosis of glucose metabolism abnormalities in Asian Indians.